ios - 在特定时间向视频添加文本层

Question

我想为视频的最后 4 秒添加一个文本层。这是我到目前为止所拥有的:

// 1 - Set up the watermark text layer
    CATextLayer *waterMarkText = [[CATextLayer alloc] init];
    [waterMarkText setFont:@"Helvetica-Neue"];
    [waterMarkText setFontSize:30];
    [waterMarkText setFrame:CGRectMake(0, 0, self.size.width, 80)];
    [waterMarkText setString:@"made with Videofy"];
    [waterMarkText setAlignmentMode:kCAAlignmentRight];
    [waterMarkText setForegroundColor:[[UIColor whiteColor] CGColor]];

//Fade In the watermark
    CABasicAnimation *fadeInAnimation = [CABasicAnimation animationWithKeyPath:@"opacity"];

    fadeInAnimation.duration = 2;
    fadeInAnimation.fromValue = [NSNumber numberWithFloat:0.0];
    fadeInAnimation.toValue = [NSNumber numberWithFloat:1.0];
    fadeInAnimation.beginTime = videoDuration - 4;
    fadeInAnimation.removedOnCompletion = NO;
    [overlayLayer addAnimation:fadeInAnimation forKey:@"animateOpacity"];

动画添加到最终视频中，但水印从视频开头可见。如何在动画开始前将不透明度设置为 0？

(我尝试将 watermarkText 的不透明度设置为 0，但这似乎覆盖了动画。)

Answer 1

因此，为了使出现和消失起作用，您需要添加两个动画 - 每个动画一个。这是一个适用于我的示例代码。在这种特殊情况下，我从视频的 0 到 1 秒添加了一个文本层。您应该为动画的开始时间设置自己的值。您应该在开始时将不透明度设置为 0。

        textLayer.opacity = 0

        let startVisible = CABasicAnimation(keyPath: "opacity")
        startVisible.duration = 0.1 // for appearing in duration
        startVisible.repeatCount = 1
        startVisible.fromValue = 0.0
        startVisible.toValue = 1.0
        startVisible.beginTime = 0.0 // overlay time range start second
        startVisible.isRemovedOnCompletion = false
        startVisible.fillMode = CAMediaTimingFillMode.forwards
        textLayer.add(startVisible, forKey: "startAnimation")

        let endVisible = CABasicAnimation(keyPath: "opacity")
        endVisible.duration = 0.1 // for disappearing in duration
        endVisible.repeatCount = 1
        endVisible.fromValue = 1.0
        endVisible.toValue = 0.0
        endVisible.beginTime = 1.0 // overlay time range end second
        endVisible.fillMode = CAMediaTimingFillMode.forwards
        endVisible.isRemovedOnCompletion = false
        textLayer.add(endVisible, forKey: "endAnimation")